US6083319A - Non-linear crystals and their applications - Google Patents
Non-linear crystals and their applications Download PDFInfo
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- US6083319A US6083319A US08/722,150 US72215097A US6083319A US 6083319 A US6083319 A US 6083319A US 72215097 A US72215097 A US 72215097A US 6083319 A US6083319 A US 6083319A
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- 239000013078 crystal Substances 0.000 title claims abstract description 78
- 239000000203 mixture Substances 0.000 claims abstract description 15
- 238000002425 crystallisation Methods 0.000 claims abstract description 10
- 230000008025 crystallization Effects 0.000 claims abstract description 10
- 229910052688 Gadolinium Inorganic materials 0.000 claims abstract description 9
- 229910052788 barium Inorganic materials 0.000 claims abstract description 9
- 229910052747 lanthanoid Inorganic materials 0.000 claims abstract description 9
- 150000002602 lanthanoids Chemical class 0.000 claims abstract description 9
- 229910052712 strontium Inorganic materials 0.000 claims abstract description 9
- 229910052727 yttrium Inorganic materials 0.000 claims abstract description 9
- 229910052746 lanthanum Inorganic materials 0.000 claims abstract description 8
- 229910052765 Lutetium Inorganic materials 0.000 claims abstract description 7
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 7
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 claims description 16
- 230000009021 linear effect Effects 0.000 claims description 15
- 238000002844 melting Methods 0.000 claims description 15
- 230000008018 melting Effects 0.000 claims description 15
- 238000000034 method Methods 0.000 claims description 12
- 239000000463 material Substances 0.000 claims description 6
- 230000003287 optical effect Effects 0.000 claims description 5
- 229910052779 Neodymium Inorganic materials 0.000 claims description 4
- 239000004327 boric acid Substances 0.000 claims description 3
- 239000002994 raw material Substances 0.000 claims 4
- GGZZISOUXJHYOY-UHFFFAOYSA-N 8-amino-4-hydroxynaphthalene-2-sulfonic acid Chemical compound C1=C(S(O)(=O)=O)C=C2C(N)=CC=CC2=C1O GGZZISOUXJHYOY-UHFFFAOYSA-N 0.000 claims 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 claims 2
- 239000000155 melt Substances 0.000 claims 2
- 229910052751 metal Inorganic materials 0.000 claims 2
- 239000002184 metal Substances 0.000 claims 2
- 150000002739 metals Chemical class 0.000 claims 2
- 230000000694 effects Effects 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 4
- 235000019796 monopotassium phosphate Nutrition 0.000 description 4
- 229910003327 LiNbO3 Inorganic materials 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 230000010287 polarization Effects 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 238000006467 substitution reaction Methods 0.000 description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- -1 alkaline-earth metal carbonates Chemical class 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- BTBUEUYNUDRHOZ-UHFFFAOYSA-N Borate Chemical compound [O-]B([O-])[O-] BTBUEUYNUDRHOZ-UHFFFAOYSA-N 0.000 description 1
- 238000001691 Bridgeman technique Methods 0.000 description 1
- 229910003887 H3 BO3 Inorganic materials 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000008033 biological extinction Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 1
- 230000005281 excited state Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- UIWYJDYFSGRHKR-UHFFFAOYSA-N gadolinium atom Chemical compound [Gd] UIWYJDYFSGRHKR-UHFFFAOYSA-N 0.000 description 1
- 230000000977 initiatory effect Effects 0.000 description 1
- 229910052741 iridium Inorganic materials 0.000 description 1
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 1
- 229910021644 lanthanide ion Inorganic materials 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 229910000402 monopotassium phosphate Inorganic materials 0.000 description 1
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 description 1
- 230000009022 nonlinear effect Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 230000003071 parasitic effect Effects 0.000 description 1
- PJNZPQUBCPKICU-UHFFFAOYSA-N phosphoric acid;potassium Chemical compound [K].OP(O)(O)=O PJNZPQUBCPKICU-UHFFFAOYSA-N 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000004857 zone melting Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/355—Non-linear optics characterised by the materials used
- G02F1/3551—Crystals
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/37—Non-linear optics for second-harmonic generation
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/39—Non-linear optics for parametric generation or amplification of light, infrared or ultraviolet waves
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
- H01S3/109—Frequency multiplication, e.g. harmonic generation
- H01S3/1095—Frequency multiplication, e.g. harmonic generation self doubling, e.g. lasing and frequency doubling by the same active medium
Definitions
- the invention relates to crystals for non-linear optics, to the fabrication of these crystals and to the applications of these crystals.
- KDP potassium dihydrogen phosphate
- the invention therefore proposes the production of crystals for non-linear optics from their molten constituents, their melting being congruent.
- the invention also proposes the use of these non-linear crystals, in particular as frequency doublers or mixers or as optical parametric oscillators.
- the invention further proposes the use of these crystals incorporating an effective quantity of an ion for generating a laser effect for the purpose of producing self-frequency-doubling laser crystals.
- M is Ca, or Ca partially substituted with Sr or Ba;
- Ln is one of the lanthanides of the group comprising Y, Gd, La and Lu.
- x is preferably less than 0.5 and, even better, less than 0.30.
- y is preferably less than 0.5 and, even better, less than 0.3.
- the choice of lanthanide may advantageously be determined depending on the projected use. This is because the non-linear coefficients and the birefringence of the material depend on the rare earth inserted into the matrix.
- the crystals according to the invention may, as indicated previously, be doped by means of optically active lanthanide ions, such as Nd 3+ .
- optically active lanthanide ions such as Nd 3+ .
- z depends on the desired effect, knowing that the presence of substituent elements may lead to competition between the effects induced. The consequence of increasing the concentration is firstly to increase the laser effect. Above a certain concentration of substitution ions, progressive extinction of the emission is observed. The substituted ions become too "close” to one another and interact. In practice, substitution does not exceed 20%, and preferably not 10%. In other words, z is preferably less than 0.2 and advantageously less than 0.1. In general, the concentration is such that the lifetime is not shorter than half the maximum lifetime observable at low concentration, i.e. 99 microseconds.
- non-linear crystals used according to the invention are advantageously obtained using a method of the Czochralski or Bridgman type. Any other crystal-growing method using melting may be suitable, in particular zone melting, which enables small-diameter single-crystal fibres to be obtained.
- the molten baths are obtained from oxides of lanthanides, Ln 2 O 3 , suitable alkaline-earth metal carbonates MCO 3 and boric acid or anhydride.
- the constituents, in powder form, are intimately mixed and heated to a temperature sufficient to ensure melting of the mixture. This temperature is maintained until the mixture is completely homogeneous.
- the molten bath is then brought down to the crystallization temperature, which makes it possible to initiate the formation of a single crystal.
- Nd-doped cristals The method of forming Nd-doped cristals is identical.
- the mixture of oxides of lanthanides is simply substituted for the lanthanide alone.
- the initial mixture is produced by means of 107 g of Gd 2 O 3 , 236 g of CaCO 3 and 109 g of H 3 BO 3 , constituting an approximately 300 g charge of oxides.
- the mixture made is placed in an approximately 100 cm 3 iridium crucible in an inert atmosphere or in an approximately 100 cm 3 platinum crucible in oxygen.
- the temperature is raised to 1550° C. and held there for 2 hours. It is then brought down to approximately the congruent melting temperature (1480° C.).
- a seed of suitably chosen crystallographic orientation is fixed on a rod which can rotate about its axis. The seed is brought into contact with the surface of the bath.
- the rod rotates about its axis at between 33 and 45 rpm.
- the rod After a crystallization initiation period, the rod, still rotating, is moved translationally at about 0.5 mm/h for the first three hours, and then at 2.5 mm/h.
- the uniform growth of the single crystal is interrupted when the cylinder formed is 8 cm in length, for a diameter of 2 cm. It is brought down to room temperature in 72 hours.
- the single crystal formed exhibits very good homogeneity, with no inclusion of bubbles. It has a hardness of 6.5 Mohs.
- the other crystals according to the invention are prepared according to the same techniques.
- the observed congruent melting points lie within the 1400 to 1500° C. temperature range.
- the crystals obtained are mechanically strong and chemically resistant. They exhibit the property of being non-hygroscopic. In addition, they lend themselves suitably to subsequent cutting and polishing operations. Their structure is monoclinical with no centre of symmetry (Cm space group).
- the gadolinium crystal is transparent in the 0.35-3 micrometre range.
- the transparency window is 0.22-3 micrometres.
- the refractive indices as a function of wavelength are determined using the minimum deviation method. They are established in the given way in the following table for the Ca 4 GdO(BO 3 ) 3 crystal:
- the phase matching for frequency doubling may be obtained for incident wavelengths lying between 0.87 ⁇ m and 3 ⁇ m. It is only of type I (at the fundamental frequency, the two photons have the same polarization) for the 1.064 ⁇ m wavelength of an Nd-doped YAG laser; it is either of type I or of type II (at the fundamental frequency, the two photons have orthogonal polarizations) for wavelengths lying between 1.064 and 3 ⁇ m.
- the type-I phase matching angles at 1.064 ⁇ m are:
- the value of the effective non-linear coefficient d eff measured in the ZX plane, within the 788-1456 nm fundamental wavelength range, represents 40 to 70% of that of the d eff of BBO.
- the Ca 4 GdO(BO 3 ) 3 crystal When exposed to the light flux of a 1.064 ⁇ m YAG laser (6 ns), the Ca 4 GdO(BO 3 ) 3 crystal exhibits a damage threshold close to 1 GW/cm 2 , comparable to that of BBO under the same conditions.
- the walk-off angle of Ca 4 GdO(BO 3 ) 3 is 0.7° (i.e. 13 mrd), that is one fifth of that of BBO (4°, i.e. 70 mrd).
- the conversion rate from the first to the second harmonic reaches a value of 55%.
- the crystals produce a stable response.
- the Ca 4 GdO(BO 3 ) 3 crystals represent a novel material endowed with excellent non-linear properties.
- These crystals may also serve to obtain the sum or difference of frequencies between two laser beams and to constitute optical parametric oscillators.
- the crystals studied above have formed the subject of Nd-doping.
- the inventors have studied the properties of an Nd-doped Ca 4 GdO(BO 3 ) 3 single crystal.
- the crystals prepared as above were substituted for 5% of the Gd with Nd.
- the doped crystal offers the advantage of a very low absorption for wavelengths corresponding to the second harmonic, contrary to that which is observed, for example, for crystals developed hitherto for forming doubling lasers, such as Nd-doped YAl 3 (BO 3 ) 4 (NYAB) crystals which exhibit a significant absorption at 531 nm.
- Nd-doped YAl 3 (BO 3 ) 4 (NYAB) crystals which exhibit a significant absorption at 531 nm.
- the absorption spectrum exhibits a wide band centred on 810 nm, the effective cross-section of which is measured at 1.5 ⁇ 10 -20 cm 2 .
- the emission from the doped crystal for the 4 F 3/2 ⁇ 4 1 11/2 transition is at the 1060 nm wavelength, with an effective emission cross-section of 1.7 ⁇ 10 -20 cm 2 .
- the lifetime of the excited state is 95 microseconds.
- the frequency doubling produces radiation at 530 nm, therefore outside the intense absorption zones of the crystal. For this reason, the self-frequency-doubling lasers according to the invention make it possible to obtain very high intensity of this second harmonic.
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- Crystallography & Structural Chemistry (AREA)
- Nonlinear Science (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Inorganic Chemistry (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
- Lasers (AREA)
- Saccharide Compounds (AREA)
- Pharmaceuticals Containing Other Organic And Inorganic Compounds (AREA)
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Abstract
Non-linear single crystal obtained by crystallization of a congruent molten composition of general formula:
M.sub.4 LnO(BO.sub.3).sub.3
in which:
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one of the lanthanides of the group comprising Y, Gd, La and Lu.
Description
1. Field of the Invention
The invention relates to crystals for non-linear optics, to the fabrication of these crystals and to the applications of these crystals.
2. Discussion of the Background
The crystals used in non-linear optics belong to various families, each exhibiting quite specific properties. Historically, one of the first products which appeared in this field was potassium dihydrogen phosphate (KDP). This material is still very widely used because of the relative ease of fabrication, and consequently its relatively low cost. On the other hand, KDP is very sensitive to water, which means that there are several constraints on the way in which it is used. Its second harmonic coefficient is small, which results in relatively low emission of frequency-doubled radiation. Although KDP may easily form good-sized single crystals, which may be required when it is necessary to be able to handle relatively high powers, most crystals for non-linear optics are of small size in practice. This is because they are usually produced by flux-determined growth. This is the case for BBO, LBO and KTP. In this mode, growth is very slow, requiring several weeks or even several months to reach sizes suitable for most uses.
It has been proposed to form crystals by congruent melting, using the Czochralski or Bridgman-Stockbarger techniques. This is the case, for example, for LiNbO3 crystals. LiNbO3 crystals exhibit the property of being photorefractive which, for secondharmonic generation, is a drawback. Finally, LiNbO3 crystals are very brittle. LaBGeO5 may also be formed by melting. However, it is difficult to obtain because of the appearance of undesirable phases, unless the crystallization operation is perfectly controlled. Moreover, this crystal provides only a relatively low non-linear susceptibility coefficient.
The invention therefore proposes the production of crystals for non-linear optics from their molten constituents, their melting being congruent. The invention also proposes the use of these non-linear crystals, in particular as frequency doublers or mixers or as optical parametric oscillators. The invention further proposes the use of these crystals incorporating an effective quantity of an ion for generating a laser effect for the purpose of producing self-frequency-doubling laser crystals.
According to the invention, the materials employed satisfy the general formula:
M.sub.4 LnO (BO.sub.3).sub.3
in which:
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one of the lanthanides of the group comprising Y, Gd, La and Lu.
In the case of Ca partially substituted with Sr or Ba, this substitution is limited to the content for which parasitic phases may develop in the molten bath during crystallization, in other words limited to values for which the M4 LnO(BO3)3 phase no longer exhibits congruent melting.
For compounds of the type:
Ca.sub.4-x Sr.sub.x LnO (BO.sub.3).sub.3
x is preferably less than 0.5 and, even better, less than 0.30.
For compounds of the type:
Ca.sub.4-y Ba.sub.y LnO (BO.sub.3).sub.3
y is preferably less than 0.5 and, even better, less than 0.3.
The choice of lanthanide may advantageously be determined depending on the projected use. This is because the non-linear coefficients and the birefringence of the material depend on the rare earth inserted into the matrix.
The crystals according to the invention may, as indicated previously, be doped by means of optically active lanthanide ions, such as Nd3+. The crystals in question are of formula:
M.sub.4 Ln.sub.1-z Nd.sub.z O (BO.sub.3).sub.3
in which:
M and Ln have the meanings indicated above,
z depends on the desired effect, knowing that the presence of substituent elements may lead to competition between the effects induced. The consequence of increasing the concentration is firstly to increase the laser effect. Above a certain concentration of substitution ions, progressive extinction of the emission is observed. The substituted ions become too "close" to one another and interact. In practice, substitution does not exceed 20%, and preferably not 10%. In other words, z is preferably less than 0.2 and advantageously less than 0.1. In general, the concentration is such that the lifetime is not shorter than half the maximum lifetime observable at low concentration, i.e. 99 microseconds.
The non-linear crystals used according to the invention are advantageously obtained using a method of the Czochralski or Bridgman type. Any other crystal-growing method using melting may be suitable, in particular zone melting, which enables small-diameter single-crystal fibres to be obtained.
The molten baths are obtained from oxides of lanthanides, Ln2 O3, suitable alkaline-earth metal carbonates MCO3 and boric acid or anhydride. The constituents, in powder form, are intimately mixed and heated to a temperature sufficient to ensure melting of the mixture. This temperature is maintained until the mixture is completely homogeneous. The molten bath is then brought down to the crystallization temperature, which makes it possible to initiate the formation of a single crystal.
The method of forming Nd-doped cristals is identical. The mixture of oxides of lanthanides is simply substituted for the lanthanide alone.
The invention will be described in more detail below, especially with reference to Ca4 GdO(BO3)3 crystals.
The initial mixture is produced by means of 107 g of Gd2 O3, 236 g of CaCO3 and 109 g of H3 BO3, constituting an approximately 300 g charge of oxides. The mixture made is placed in an approximately 100 cm3 iridium crucible in an inert atmosphere or in an approximately 100 cm3 platinum crucible in oxygen. The temperature is raised to 1550° C. and held there for 2 hours. It is then brought down to approximately the congruent melting temperature (1480° C.). A seed of suitably chosen crystallographic orientation is fixed on a rod which can rotate about its axis. The seed is brought into contact with the surface of the bath.
The rod rotates about its axis at between 33 and 45 rpm.
After a crystallization initiation period, the rod, still rotating, is moved translationally at about 0.5 mm/h for the first three hours, and then at 2.5 mm/h.
The uniform growth of the single crystal is interrupted when the cylinder formed is 8 cm in length, for a diameter of 2 cm. It is brought down to room temperature in 72 hours.
The single crystal formed exhibits very good homogeneity, with no inclusion of bubbles. It has a hardness of 6.5 Mohs.
The other crystals according to the invention are prepared according to the same techniques. The observed congruent melting points lie within the 1400 to 1500° C. temperature range.
The crystals obtained are mechanically strong and chemically resistant. They exhibit the property of being non-hygroscopic. In addition, they lend themselves suitably to subsequent cutting and polishing operations. Their structure is monoclinical with no centre of symmetry (Cm space group).
The crystallographic characteristics of Ca4 GdΩ(BO3)3 are:
a=8.092 Å
b=16.007 Å
c=3.561 Å
β=101.2°
Z=4
density d=3.75.
The orientations of the crystallophysical axes X, Y, Z with respect to the crystallographic axes a, b, c are:
(Z, a)=26°
(Y, b)=0°
(X, c)=15°.
The angle (V, z) between the optical axis and the Z axis is such that 2 (V, z)=120.66°, which defines the crystal as being a negative biaxial crystal.
The gadolinium crystal is transparent in the 0.35-3 micrometre range. For the yttrium compound, the transparency window is 0.22-3 micrometres.
The refractive indices as a function of wavelength are determined using the minimum deviation method. They are established in the given way in the following table for the Ca4 GdO(BO3)3 crystal:
______________________________________ (μm) n.sub.x n.sub.y n.sub.z ______________________________________ 0.4047 1.7209 1.7476 1.7563 0.4358 1.7142 1.7409 1.7493 0.4678 1.7089 1.7350 1.7436 0.4800 1.7068 1.7333 1.7418 0.5090 1.7033 1.7295 1.7379 0.5461 1.6992 1.7253 1.7340 0.5780 1.6966 1.7225 1.7310 0.5876 1.6960 1.7218 1.7303 0.6439 1.6923 1.7181 1.7265 0.6678 1.6910 1.7168 1.7250 0.7290 1.6879 1.7133 1.7216 0.7960 1.6860 1.7112 1.7197 ______________________________________
From the experimental values above, the Sellmeier formulae have been established:
n.sup.2.sub.z =2.9222+0.02471/(λ.sup.2 -0.01279)-0.00820 λ.sup.2
n.sup.2.sub.y =2.8957+0.02402/(λ.sup.2 -0.01395)-0.01039 λ.sup.2
n.sup.2.sub.x =2.8065+0.02347/(λ.sup.2 -0.01300)-0.00356 λ.sup.2
By way of example, the phase matching for frequency doubling may be obtained for incident wavelengths lying between 0.87 μm and 3 μm. It is only of type I (at the fundamental frequency, the two photons have the same polarization) for the 1.064 μm wavelength of an Nd-doped YAG laser; it is either of type I or of type II (at the fundamental frequency, the two photons have orthogonal polarizations) for wavelengths lying between 1.064 and 3 μm.
For the borate studied, the type-I phase matching angles at 1.064 μm are:
θ .O slashed.
(x, y) plane 90° 46.3°
(x, z) plane 19.3° 0°
The non-linear coefficients have been determined using the so-called "phase matching angle" method, by comparison with a standard crystal in the principal planes. The ZX plane has given the best performance. Thus:
d12 =0.56 pm/V
d32 =0.44 pm/V.
The value of the effective non-linear coefficient deff measured in the ZX plane, within the 788-1456 nm fundamental wavelength range, represents 40 to 70% of that of the deff of BBO.
When exposed to the light flux of a 1.064 μm YAG laser (6 ns), the Ca4 GdO(BO3)3 crystal exhibits a damage threshold close to 1 GW/cm2, comparable to that of BBO under the same conditions.
The angular acceptance of Ca4 GdO(BO3)3 is 2.15 mrd.cm, much higher than that of BBO (1.4 mrd).
The walk-off angle of Ca4 GdO(BO3)3 is 0.7° (i.e. 13 mrd), that is one fifth of that of BBO (4°, i.e. 70 mrd).
The conversion rate from the first to the second harmonic reaches a value of 55%. The crystals produce a stable response.
In view of the characteristics of Ca4 GdO(BO3)3 described above, the Ca4 GdO(BO3)3 crystals represent a novel material endowed with excellent non-linear properties.
From the estimated effective non-linear coefficient (deff), which is between 0.4 and 0.7 times that of BBO, the effectiveness of the non-linear process in Ca4 GdO(BO3)3 should be exceptional insofar as it is possible to produce from it large-sized single crystals using the Czochralski method.
Production of single crystals in a relatively rapid manner and for a moderate cost, combined with the previously mentioned characteristics, allows them to be suitably used in various applications. Among these applications, the most usual relate to the frequency doubling of laser beams, especially those emitting in the infrared, giving rise to radiation in the visible.
These crystals may also serve to obtain the sum or difference of frequencies between two laser beams and to constitute optical parametric oscillators.
Still by way of example of application, the crystals studied above have formed the subject of Nd-doping. In particular, the inventors have studied the properties of an Nd-doped Ca4 GdO(BO3)3 single crystal. The crystals prepared as above were substituted for 5% of the Gd with Nd.
The doped crystal offers the advantage of a very low absorption for wavelengths corresponding to the second harmonic, contrary to that which is observed, for example, for crystals developed hitherto for forming doubling lasers, such as Nd-doped YAl3 (BO3)4 (NYAB) crystals which exhibit a significant absorption at 531 nm.
The absorption spectrum exhibits a wide band centred on 810 nm, the effective cross-section of which is measured at 1.5×10-20 cm2.
The emission from the doped crystal for the 4 F3/2 →4 111/2 transition is at the 1060 nm wavelength, with an effective emission cross-section of 1.7×10-20 cm2.
For a 5% Nd doping level, the lifetime of the excited state is 95 microseconds.
The laser tests carried out on a Ca4 GdO(BO3)3 crystal doped with neodymium and cut along the crystallophysical axes X, Y and Z have led to the observation of the laser effect at 1060 nm, with the following characteristics:
______________________________________ Direction of Threshold Differential Polarization propagation of power yield of the emitted the pump beam (mW) (%) laser beam ______________________________________ X 288 29 E//Z Y 125 34 E//X Z 210 29 E//X ______________________________________
The frequency doubling produces radiation at 530 nm, therefore outside the intense absorption zones of the crystal. For this reason, the self-frequency-doubling lasers according to the invention make it possible to obtain very high intensity of this second harmonic.
The examples indicated above are not limiting in character. They are given by way of illustration of the invention in some of its embodiments. They are sufficient to show the advantages provided by the invention of crystals which are relatively inexpensive, of large size and providing useful properties as frequency doublers or mixers, optical parametric oscillators or as self-doubling lasers.
Claims (14)
1. Non-linear single crystal obtained by crystallization of a congruent molten composition of general formula:
M.sub.4 LnO(BO.sub.3).sub.3
in which:
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one of the lanthanides of the group comprising Y, Gd, La and Lu
wherein, in the general formula of which, when Ca is partially substituted with Sr or Ba, the content of the substituted element is limited to that for which the melting is no longer congruent.
2. Non-linear single crystal obtained by crystallization of a congruent molten composition, of general formula:
Ca.sub.4-x Sr.sub.x LnO(BO.sub.3).sub.3
in which x is less than 0.5.
3. Non-linear single crystal obtained by crystallization of a congruent molten composition, of general formula:
Ca.sub.4-y Ba.sub.y LnO(BO.sub.3).sub.3
in which y is less than 0.5.
4. Non-linear single crystal obtained by crystallization of a congruent molten composition of general formula:
M.sub.4 LnO(BO.sub.3).sub.3
in which:
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one of the lanthanides of the group comprising Y, Gd, La and Lu, the said crystal being doped and satisfying the general formula:
M.sub.4 Ln.sub.1-z Nd.sub.z O(BO.sub.3).sub.3
in which:
M and Ln have the meanings indicated above;
z is at most equal to 0.2.
5. In a self-frequency-doubling laser containing a crystal, the improvement wherein the crystal is the single crystal according to claim 4 and contains Nd, wherein M is Ca, and Ln is Gd or La.
6. A method of preparing a non-linear single crystal comprising:
(a) providing a bath of a congruent molten composition of the formula
M.sub.4 LnO(BO.sub.3).sub.3
from oxides of Ln, carbonates of M, and boric acid, as raw materials, by melting the raw materials in a high temperature resistant material at a higher temperature than the congruent melting temperature of the crystal, wherein
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one of the lanthanides selected from the group consisting of Y, Gd, La, and Lu;
(b) bringing the melt down to approximately the congruent melting temperature of the crystal;
(c) adding a seed with a suitably chosen crystallographic orientation;
(d) fixing the seed on a rotating rod;
(e) bringing the seed into contact with a surface of the bath;
(f) moving the rod translationally and forming the single crystal.
7. Non-linear single crystal obtained by crystallization of a congruent molten composition of general formula:
M.sub.4 LnO(BO.sub.3).sub.3
in which
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one or a mixture of metals selected from the group consisting of Y, La, Gd, Nd and Lu.
8. A method of preparing a non-linear single crystal comprising:
(a) providing a bath of a congruent molten composition of the formula
M.sub.4 LnO(BO.sub.3).sub.3
from oxides of Ln, carbonates of M, and boric acid, as raw materials, by melting the raw materials in a high temperature resistant material at a higher temperature than the congruent melting temperature of the crystal, wherein
M is Ca, or Ca partially substituted with Sr or Ba;
Ln is one or a mixture of metals selected from the group consisting of Y, La, Gd, Nd and Lu;
(b) bringing the melt down to approximately the congruent melting temperature of the crystal;
(c) adding a seed with a suitably chosen crystallographic orientation;
(d) fixing the seed on a rotating rod;
(e) bringing the seed into contact with a surface of the bath;
(f) moving the rod translationally and forming the single crystal;
(g) bringing the single crystal down to room temperature.
9. Non-linear single crystal obtained by the method of claim 6.
10. Non-linear single crystal obtained by the method of claim 8.
11. The non-linear single crystal of claim 7, and having a length of at least 8 cm, or a diameter of at least 2 cm, or both.
12. In a frequency doubler containing a crystal, the improvement wherein the crystal is the single crystal according to claim 7.
13. In an optical parametric oscillator containing a crystal, the improvement wherein the crystal is the single crystal according to claim 7.
14. In a frequency mixer for two lasers containing a crystal, the improvement wherein the crystal is the single crystal according to claim 7.
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FR9501963A FR2730828B1 (en) | 1995-02-21 | 1995-02-21 | NON-LINEAR CRYSTALS AND THEIR APPLICATIONS |
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PCT/FR1996/000255 WO1996026464A1 (en) | 1995-02-21 | 1996-02-16 | Non-linear crystals and uses thereof |
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EP (1) | EP0756719B1 (en) |
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FR (1) | FR2730828B1 (en) |
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Cited By (8)
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US6551528B1 (en) * | 1998-03-27 | 2003-04-22 | Japan Science And Technology Corporation | Wavelength conversion crystal and method for generating laser beam, and apparatus for generating laser beam |
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US20050190805A1 (en) * | 2003-06-30 | 2005-09-01 | Scripsick Michael P. | Doped stoichiometric lithium niobate and lithium tantalate for self-frequency conversion lasers |
US20070108425A1 (en) * | 2002-10-01 | 2007-05-17 | The Regents Of The University Of California | Nonlinear optical crystal optimized for Ytterbium laser host wavelengths |
US20070164630A1 (en) * | 2006-01-17 | 2007-07-19 | Shujun Zhang | High temperature piezoelectric material |
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US20070108425A1 (en) * | 2002-10-01 | 2007-05-17 | The Regents Of The University Of California | Nonlinear optical crystal optimized for Ytterbium laser host wavelengths |
US7378042B2 (en) | 2002-10-01 | 2008-05-27 | Lawrence Livermore National Security, Llc | Nonlinear optical crystal optimized for Ytterbium laser host wavelengths |
US7260124B1 (en) | 2002-10-01 | 2007-08-21 | The Regents Of The University Of California | Nonlinear optical crystal optimized for ytterbium laser host wavelengths |
US20050190805A1 (en) * | 2003-06-30 | 2005-09-01 | Scripsick Michael P. | Doped stoichiometric lithium niobate and lithium tantalate for self-frequency conversion lasers |
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US7622851B2 (en) | 2006-01-17 | 2009-11-24 | The Penn State Research Foundation | High temperature piezoelectric material |
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Also Published As
Publication number | Publication date |
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RU2169802C2 (en) | 2001-06-27 |
JP3875265B2 (en) | 2007-01-31 |
HU219305B (en) | 2001-03-28 |
DE69629770D1 (en) | 2003-10-09 |
FR2730828B1 (en) | 1997-04-30 |
WO1996026464A1 (en) | 1996-08-29 |
HUP9602910A3 (en) | 1998-04-28 |
HUP9602910A2 (en) | 1997-05-28 |
EP0756719A1 (en) | 1997-02-05 |
CN1146812A (en) | 1997-04-02 |
FR2730828A1 (en) | 1996-08-23 |
CN1150427C (en) | 2004-05-19 |
DE69629770T2 (en) | 2004-07-01 |
EP0756719B1 (en) | 2003-09-03 |
PL316947A1 (en) | 1997-02-17 |
JPH09512354A (en) | 1997-12-09 |
ATE249061T1 (en) | 2003-09-15 |
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